Video display devices with use of an LED backlight for illuminating a display panel have been widely used. The LED backlight has an advantage that a local dimming function is available. With the local dimming function, a backlight is divided into a plurality of areas, and light emission of an LED is controlled for each of the areas in accordance with a video signal from a display area corresponding to each of the areas. For example, it becomes possible to perform control so that light emission of an LED is suppressed for a dark part in a screen while light emission of the LED is produced strongly for a bright part in the screen. This makes it possible to reduce power consumption of the backlight and increase contrast in a display screen.
For example, an example of conventional local dimming control is shown in FIG. 26. In the figure, a backlight is divided into eight areas and luminance of an LED is controlled in accordance with a maximum tone value of a video signal corresponding to each of the areas. The maximum tone value of the video signal in each of the areas is provided as shown in FIG. 26(A). The letters A to H denote the numbers of the areas, and the numbers given below them of which indicate the maximum tone values in the respective areas are given in numbers.
For example, the luminance of the LED in the respective areas by local dimming is given as shown in FIG. 26(B). In other words, the luminance of the LED is controlled for each of the areas in accordance with a video signal in each of the areas. In this case, a video is represented relatively dark in an area where a maximum tone value of a video signal is low, and thus the luminance of the LED is lowered so as to reduce generation of black float to increase contrast and power consumption of the LED is sought to be reduced. In this case, the maximum luminance in each of the areas is limited to luminance when all LEDs of the backlight are lighted by the duty ratio of 100% (for example, 450 cd/m2).
Regarding a technology of performing lighting control of a backlight in accordance with an input video signal, for example, Patent Literature 1 discloses a method of controlling a peak luminance level in order to reduce flicker and a moving image blur even when a light emission period is varied over a wide range. In the control method, when setting illumination periods of a display panel whose peak luminance level is varied by controlling a total illumination period length as the total of the illumination periods set within a field period, a light emission mode is determined based on an average luminance level of the entire screen. Then the number, set positions and period lengths of the illumination periods set within one-field period are set under setting conditions prescribed as to the determined light emission mode so as to obtain the peak luminance level set according to input image data.